WO2008113866A1

WO2008113866A1 - Electrical equipment insulated with a biodegradable dielectric fluid

Info

Publication number: WO2008113866A1
Application number: PCT/ES2007/000149
Authority: WO
Inventors: Alberto Sanchez De Lema
Original assignee: Alberto Sanchez De Lema
Priority date: 2007-03-16
Filing date: 2007-03-16
Publication date: 2008-09-25
Also published as: PT2128874E; EP2128874B1; PL2128874T3; EP2128874A4; ES2423480T3; EP2128874A1

Abstract

The invention relates to the field involving the insulation and refrigeration of electrical systems. More specifically, the invention relates to piece of electrical equipment including a biodegradable dielectric fluid that is highly resistant to oxidation, consisting of an oil or a mixture of vegetable oils having a very high oleic acid content, with substantially all of the natural tocopherols thereof being conserved, and containing a metal deactivator.

Description

ELECTRICAL EQUIPMENT ISOLATED WITH DIELECTRIC FLUID

BIODEGRADABLE

FIELD OF THE INVENTION The present invention belongs to the field of insulation and cooling of electrical systems, in particular, it refers to an electrical equipment comprising a biodegradable dielectric fluid of high oxidation resistance consisting of an oil or a mixture of vegetable oils With a very high oleic acid content that substantially conserves all its natural tocopherols and contains a metal deactivator.

BACKGROUND OF THE INVENTION

Generally, the dielectric fluids that are used in the electrical industry consist of gases or liquids whose most important mission is to achieve electrical insulation between live parts, as well as to serve as a cooling medium. Liquids that are used as dielectric media can have different origins.

The liquids most used as dielectric fluids are mineral oils derived from petroleum. The great use of mineral oils is due to its low cost and easy availability, as well as its dielectric, cooling properties, low viscosity at high temperatures and excellent performance at very low temperatures. They also have a high oxidation stability. But on the other hand, mineral oils have the disadvantage that due to their chemical composition, their biodegradability is very low, so that a spill of said oil can cause damage to the ecosystem and can last in the environment for many years. Likewise, mineral oils have a high combustion power and have a very low fire point, so they pose a high risk in case of fire and / or explosion. Current regulations also require that any dielectric fluid intended for use as a refrigerant must not be classified as flammable. Depending on the use of the fluid and the degree of risk, one or more safety measures may be required. A recognized safety option is the replacement of mineral oils with less flammable or non-flammable liquids. Less flammable liquids must have a fire point equal to or greater than 300 ⁰ C. In this way, dielectric liquids with high fire point (equal to or greater than 300 ⁰ C) are sometimes used, such as silicone oils, high molecular weight hydrocarbons (HMWH) or synthetic esters. However, silicone oils and high molecular weight hydrocarbons (HMWH) are characterized, like mineral oils, by their zero or low biodegradability. Also, all these liquids have a higher cost than mineral oils.

Among the alternatives to the above-mentioned liquids that have been appearing in recent years, the natural esters from vegetable oils should be highlighted. Natural esters are obtained from oils of vegetable origin through appropriate refining and purification processes.

Vegetable oils are mainly composed of triacylglycerols, and other components in a smaller proportion such as monoacylglycerols, diacylglycerols, free fatty acids, phosphatides, sterols, oil soluble vitamins, tocopherols, pigments, waxes, long chain alcohols etc.

The triacylglycerols that appear in vegetable oils are triesters formed by three fatty acids chemically linked to glycerin. The general formula of a triacylglycerol is:

where R, R, R can be the same or different fatty acids with carbon chains from C ₁₄ to C ₂₂ normally and with saturation levels of O to 3.

The main differences between the different vegetable oils are caused by the different fatty acid contents present in the composition of their triacylglycerols.

There are several fatty acids, including myristic, palmitic, stearic, oleic, linoleic, linolenic, arachidic, eicosenoic, behenic, erucic, palmiolitic, docosadienoic, lignospheric, tetracosenoic, margaric, margaroleic, gadoleic, caprilic, capric, laphanic, lauric or lauric acids. . They differ between them by the number of carbon atoms and by the number of unsaturations (carbon-carbon double bonds)

The three fatty acids in a triacylglycerol molecule can be all the same or they can be two or three different fatty acids. The fatty acid composition of triacylglycerols varies between plant species and less among strains of a particular species. Vegetable oils derived from a single strain have essentially the same fatty acid composition in their triacylglycerols. Each triacylglycerol has unique properties depending on the fatty acids it contains.

For example, some triacylglycerols are more susceptible to oxidation than others. In this sense, oils formed by triacylglycerols with mono-unsaturated fatty acids (with a single double bond C = C) have a greater oxidation stability than oils formed by triacylglycerols with two or three carbon-carbon double bonds. Likewise, the oils formed by triacylglycerols with saturated fatty acids (no double bond C = C) will have an oxidation stability even greater than the mono-unsaturated ones but their minimum flow temperature would be much higher.

The greatest advantages of using vegetable oils as dielectric fluids are summarized in their excellent biodegradability, their obtaining from renewable natural sources, their non-toxicity, their high point of fire (~ 360 ⁰ C) and their reduced cost compared to other options with high fire point like synthetic esters. All environmental, health and safety trends have reinforced the idea of using dielectric fluids based on vegetable oils.

However, vegetable oils or their derivatives are not exempt from problems in their application as dielectric fluids in electrical equipment.

For example, the freezing point (or minimum fluidity temperature) of vegetable oils is a property to consider. The freezing point defines the temperature at which a liquid enters the solid state, with the consequent loss of cooling properties. According to the only existing standard that specifies the properties of a vegetable oil for use as a dielectric fluid, the American standard ASTM D6871-03, the freezing point must be a maximum of -10 ⁰ C. It is therefore important that the dielectric fluid It is based on vegetable oils that ensure permanence as a flowing liquid even when the dielectric fluid is subjected to moderately low temperatures (less than -15 ⁰ C).

Additives are usually used to reduce the freezing point and get dielectric liquids more resistant to low temperatures. For example, additives such as PMA (polymethacrylate), polyvinyl acetate oligomers and / or oligomers and acrylic polymers, diethylhexyl adipate, polyalkyl methacrylate have been used.

Other problematic factors in the properties of vegetable oils are the presence of water, microbial growth, the presence of solids, etc.

But in fact one of the most important problems presented by vegetable oils is that of oxidation. Vegetable oils are normally susceptible to polymerization when exposed to oxygen. The exposure to oxygen activates the unsaturated bonds present in the fatty acids of the triacylglycerols of the oils causing the oxidative polymerization of the oil, with potentially adverse effects on the properties of the dielectric fluid itself. Its susceptibility to oxidation is a strong obstacle to its use as a dielectric.

The problem of the oxidation of oils has usually been solved by adding synthetic antioxidant oils such as BHA

(butylated hydroanisole), BHT (butylated hydrotoluene), TBHQ (tertiary butylhydroquinone), THBP (tetrahydro-butro-phenyl), ascorbyl palmitate (rosemary oil), propyl gallate etc. On the other hand, the problem of the oxidation of dielectric fluids based on vegetable oils is accentuated in electrical appliances due to the catalytic activity of copper or other metals present in this type of apparatus.

All the aforementioned problems have already been raised previously in patents EP1365420, US 2004069975, US6613250, US6340658, US6645404, US6280659, JP2000090740 and JP2005317259, with disparate solutions. The inventors of the present invention propose an electrical equipment comprising a dielectric liquid that provides an alternative technical solution to the problem of oxidation and that provides very advantageous characteristics to the liquid for its application as an insulator and coolant of electrical appliances.

The solution to the problem of the oxidation of the dielectric fluid within electrical equipment comes from the use of oils with a very high content of oleic acid, and obtained by refining procedures that allow to preserve in a high percentage the natural tocopherols present in said oils vegetables, given that the traditional refining procedures entail the loss of a significant amount of their tocopherols. An example of an appropriate procedure for the purposes of the present invention is described in US patent 5928696. The inventors have discovered that certain vegetable oils with very high oleic acid content and low linoleic content and that largely retain their natural tocopherols have enough antioxidant power to avoid having to add antioxidant additives, such as non-biodegradable synthetic antioxidant additives, as it has been doing so far. The tocopherols, however, in addition to being substantially biodegradable, are substances naturally present in the composition of the oils and which have important antioxidant properties. There are four types of tocopherols α-, β-, and- and δ-tocopherol that have different antioxidant power and that occur in different proportions depending on the type of vegetable oil and the variety from which it is obtained.

In addition to solving the problem of the acceleration of oxidation due to the catalytic activity of the metals present in the electrical equipment, the inventors of the present invention provide for the incorporation of metal deactivators such as triazole, benzotriazole, dimercaptothiadiazole derivatives, etc.

OBJECT OF THE INVENTION A first object of the invention is an electrical equipment for an electrical energy distribution network comprising a tank or enclosure that integrates one or more insulated electrical elements in a biodegradable dielectric fluid free of added antioxidant additives, synthetic or not. , which comprises an oil or a mixture of vegetable oils with an oleic acid content (C18: 1) greater than 75%, a natural tocopherol content exceeding 200 ppm and incorporating a metal deactivating additive in a proportion lower than 1 % in weigh.

The second object of the invention is a method for isolating and cooling electrical elements in an energy distribution network comprising submerging or wrapping said electrical elements in a biodegradable dielectric fluid free of synthetic antioxidant additives added thereto comprising an oil or a mixture of vegetable oils with an oleic acid content (C18: 1) greater than 75%, with a natural tocopherol content greater than 200 ppm and a metal deactivating additive in a proportion lower than 1%.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates firstly to an electrical equipment for an electrical energy distribution network comprising a tank or enclosure that integrates one or more insulated electrical elements in a biodegradable dielectric fluid free of synthetic antioxidant additives added thereto comprising an oil or a mixture of vegetable oils with an oleic acid content (C18: 1) greater than 75%, characterized by having a natural tocopherol content greater than 200 ppm and a metal deactivating additive in a proportion lower than 1%. In a preferred embodiment of the invention the content of natural tocopherols of the fluid is greater than 300 ppm and in an even more preferred embodiment it is greater than 400 ppm.

In a preferred embodiment of the invention the oleic acid content of the oil or vegetable oils that make up the dielectric fluid is greater than 80% and in an even more preferred embodiment said content is greater than 90%.

Since dielectric liquids are usually in contact with metals within electrical equipment, the dielectric fluid includes as an additive a metal deactivator to prevent copper or other metal in contact with the oil from acting as a catalyst for oxidation reactions of the same. Therefore, it is suitable to include in the composition of the dielectric liquid a metal deactivator such as any derivative of triazole, benzotriazole or dimercaptothiadiazole.

In addition, the dielectric fluid incorporated in the electrical equipment of the invention preferably comprises: a) a linoleic acid (C18: 2) content of less than 3.5% b) a linolenic acid (C18: 3) content of less than 1% c) a palmitic acid (C16: 0) content of less than 4% d) a stearic acid (C18: 0) content of less than 2.5%

Especially suitable for use as a dielectric fluid in the context of the present invention are oils or mixtures of sunflower, rapeseed, soybean, cotton, jojoba, safflower, olive or olive pomace oils with high content oleic, although the preferred embodiment of the invention involves the use of high oleic sunflower oil. These oils, in addition to high levels of oleic acid, naturally possess tocopherols in a high amount that are largely lost in the normal processes of refined. The refining of said oils according to methods capable of largely conserving their natural tocopherols contributes to these oils being very suitable for use as dielectric fluids without danger of oxidation thereof. For example, the methods described in US Patent 5928696 allow to obtain oils with tocopherol concentrations greater than 400 ppm and with low phosphatide, free fatty acid and wax content.

The oil or oils resulting from the aforementioned methods can be subjected to a subsequent vacuum distillation process, using a combination of heat and vacuum, to remove a large part of its moisture. Dehumidification of the oil is necessary because the oil can have an initial level of humidity that makes it inappropriate to be used as a dielectric liquid. In this way, the vegetable oil is processed in order to eliminate excessive moisture to a level below 50 ppm.

The oils thus obtained are characterized by having induction times greater than 25 hours in Rancimat test (EN 14112) and a biodegradability index greater than 99% after 21 days (CEC-L-33-A-93). That is to say, using the aforementioned oils or their mixtures, dielectric fluids of high quality and excellent performance are achieved that meet or exceed safety standards and which in turn are not toxic, are environmentally friendly and of lower cost than other dielectric fluids. .

The dielectric fluid incorporated into the apparatus of the invention can also carry additional additives depending on the type of application to which it is to be subjected.

For applications in electrical equipment present in environments where the temperature can drop to temperatures below -15 ⁰ C it is It is advisable to add an additive to reduce the freezing point, preferably of the polyalkyl methacrylate type. The use of these additives allows to obtain dielectric fluids with freezing points equal to or lower than -18 ° C.

In a particular embodiment of the invention, the electrical equipment of the invention can be maneuver and / or protection cells, transformers, self-protected transformers with current limiting fuses or transformation centers with multiple maneuvering elements and multiple protection devices.

The second aspect of the invention relates to a method for isolating and cooling electrical elements in an energy distribution network comprising submerging or wrapping said electrical elements in a biodegradable dielectric fluid free of synthetic antioxidant additives added thereto comprising an oil or a mixture of vegetable oils with an oleic acid content (C18: 1) greater than 75%, with a natural tocopherol content greater than 200 ppm and a metal deactivating additive in a proportion lower than 1%. Obviously, all the optional and additional elements and features described herein and referring to the dielectric fluid are applicable within the method of insulating and cooling electrical elements in a distribution network described herein.

PREFERRED EMBODIMENT OF THE INVENTION

The special fatty acid composition of the triacylglycerols of the vegetable oils used and the process of obtaining them, as well as their final drying, give the resulting liquid specific physical properties that make it particularly suitable for use as a dielectric liquid. A preferred example of the invention consists of a transformer in which a dielectric liquid with the following composition is included as insulator and coolant:

Sunflower oil high in oleic acid with:

a) natural tocopherols

b) triacylglycerols, with the following fatty acid composition

c) 5000 ppm of a metal deactivating additive derived from dimercaptothiadiazole (Additin RC 8210 of Rhein Chemie) corresponding to less than 1% of the total weight of the composition.

The dielectric liquid with the composition indicated above has the following properties:

Optionally, for some more demanding embodiments, in places where the electrical equipment is subjected to extremely low temperatures, the flow temperature can be reduced further by adding an additive to the oil to obtain a lower freezing point. In this way, commercially available additives that are compatible with vegetable oils, such as the product known as Viscoplex 10-310, can be used.

Claims

1. An electrical equipment for an electric power distribution network comprising a tank or enclosure that integrates one or more insulated electrical elements in a biodegradable dielectric fluid free of synthetic antioxidant additives added thereto comprising an oil or a mixture of vegetable oils with an oleic acid (C18: 1) content exceeding 75%, with a natural tocopherols content exceeding 200 ppm and a metal deactivating additive in a proportion lower than 1%.

2. An electrical equipment according to claim 1 wherein the dielectric fluid comprises an oil or mixture of oils with an oleic acid content (C18: 1) greater than 80%.

3. An electrical equipment according to claim 1 wherein the dielectric fluid comprises an oil or mixture of oils with an oleic acid content (C18: 1) greater than 90%.

4. An electrical equipment according to claim 1 characterized in that the content of natural tocopherols of the electrical fluid is greater than 300 ppm.

5. An electrical equipment according to claim 1 characterized in that the natural tocopherol content of the dielectric fluid is greater than 400 ppm.

6. An electrical equipment according to any of the preceding claims characterized in that the dielectric fluid has a fire point greater than 350 ⁰ C.

7. An electrical equipment according to any of the preceding claims characterized in that the dielectric fluid comprises vegetable oil or oils comprises:

a) a linoleic acid (C18: 2) content of less than 3.5% b) a linolenic acid (C18: 3) content of less than 1% c) a palmitic acid (C16: 0) content of less than 4% d) a stearic acid (C18: 0) content of less than 2.5%

8. An electrical equipment according to any of the preceding claims characterized in that the dielectric fluid comprises an additive to reduce the freezing point.

9. An electrical equipment according to claim 8, characterized in that the additive is of the polyalkyl methacrylate type.

10. An electrical equipment according to claims 8 and 9, characterized in that the dielectric fluid has a freezing point equal to or less than -18 ⁰ C.

11. An electrical equipment according to any of the preceding claims wherein the metal deactivator of the dielectric fluid is a triazole, benzotriazole or dimercaptothiadiazole derivative.

12. An electrical equipment according to claim 11 wherein the metal deactivator is a derivative of dimercaptothiadiazole.

13. An electrical equipment according to any of the preceding claims, characterized in that the oil or mixture of vegetable oils of the dielectric fluid can be sunflower oil, rapeseed, soybean oil, cotton, jojoba, safflower, olive or olive pomace with high oleic content.

14. An electrical equipment according to any of the preceding claims selected from maneuver and / or protection cells, transformers, self-protected transformers with current limiting fuses or transformation centers with multiple operating elements and multiple protection devices.

15. Method for insulating and cooling electrical elements in an energy distribution network comprising submerging or wrapping said electrical elements in a biodegradable dielectric fluid free of synthetic antioxidant additives added thereto comprising an oil or a mixture of vegetable oils with a content in oleic acid (C18: 1) greater than 75%, with a natural tocopherol content exceeding 200 ppm and a metal deactivating additive in a proportion less than 1%.